1. Technical Field
This invention relates to an apparatus and method for the reproduction of holographic films from a master holographic film by a contact printing process.
2. Description of the Prior Art
In order to facilitate replication of volume transmission holograms, it is usually been required to create the original hologram on a glass plate, and then reproduce the recorded image on another glass plate. The second glass plate or the contact copy plate, is placed with emulsion side exposed to the emulsion side of the original volume hologram. An index matching fluid such as Xylene is placed between the two plates and all air is carefully expelled. The recorded image in the original hologram is then reconstructed using a coherent reference beam which should duplicate the curvature, direction, and wave length of the original reference beam used to create the original hologram. This results in a maximum efficiency undistorted reconstruction of the original subject being defracted to the second copy plate and recording of the image therein.
For efficient copying with high quality results, it is vital that the original hologram and the copy plate be in good optical contact and that the reconstruction beam have characteristics similar to the original reference beam used to create the original hologram. When both the original and contact copy holograms are glass plates, good optical contact and therefore high quality copying can be achieved. However, glass plates are rather expensive and when large holograms are desired, larger glass plates usually are not even available.
Recently, films such as Mylar have been used in place of the glass plates, since they are generally less expensive and available in large sizes for larger hologram recording. However, since the film is not perfectly flat in its natural state, it is not as easy to create high quality reproductions using the method described above for glass plates. It is also necessary that the emulsion of the original hologram and the emulsion of the copy hologram be close enough together during the exposure replication process in order to prevent a loss of resolution due to the defraction of incident light by the original hologram. Unless close contact is maintained during the exposure process, defraction in the region between the two emulsions will seriously deteriorate the fringe pattern required by the emulsion of the copy. The reconstruction of the recorded duplicated image will be substantially inferior in quality as compared to the image reconstructed from the original hologram.
It is therefore an objective of this invention to provide a simple means of creating optical contact between two pieces of film while holding them flat enough for the copying to take place, while also allowing for easy separation of the films after the duplication.
Another object of the invention is to provide for various geometries for reconstruction beams, along with a moving slit defining member that causes exposure only on the part of the films that are in close optical contact with each other.